[v3,0/4] ceph: forward average read/write/metadata latency

Message

Venky Shankar Sept. 21, 2021, 1:07 p.m. UTC

v3:
  - rework average/stdev handling by maintaining sum of squares
    and calculating standard deviation when sending metrics

Right now, cumulative read/write/metadata latencies are tracked
and are periodically forwarded to the MDS. These meterics are not
particularly useful. A much more useful metric is the average latency
and standard deviation (stdev) which is what this series of patches
aims to do.

The userspace (libcephfs+tool) changes are here::

          https://github.com/ceph/ceph/pull/41397

The math involved in keeping track of the average latency and stdev
are adjusted to closely mimic how its done in user space ceph (with
some restrictions obviously) as per::

          NEW_AVG = OLD_AVG + ((latency - OLD_AVG) / total_ops)
          NEW_STDEV = SQRT(SQ_SUM / (total_ops - 1))

Note that the cumulative latencies are still forwarded to the MDS but
the tool (cephfs-top) ignores it altogether.

Venky Shankar (4):
  ceph: use "struct ceph_timespec" for r/w/m latencies
  ceph: track average/stdev r/w/m latency
  ceph: include average/stddev r/w/m latency in mds metrics
  ceph: use tracked average r/w/m latencies to display metrics in
    debugfs

 fs/ceph/debugfs.c |   6 +--
 fs/ceph/metric.c  | 109 ++++++++++++++++++++++++----------------------
 fs/ceph/metric.h  |  62 ++++++++++++++++----------
 3 files changed, 101 insertions(+), 76 deletions(-)